Members of the PSL provide consulting services in the physical sciences and applied mathematics. Data has been analyzed on the rate at which fits develop after head injury in a group of over 400 head-injured veterans of Vietnam. We have found that three subpopulations can be identified; those who develop fits within a month post-injury, those who develop them at an exponential rate over a period of approximately five years, and those who develop them at a different nonexponential rate after approximately five years. The first two groups have been identified by previous investigators, but the third appears only in the present study and is due to the long follow-up time. A joint study with Dr. A. P. Minton has been started on the use of overspeeding to accelerate sedimentation equilibrium experiments on the ultracentrifuge.